Using a fishing rod, players can transport animals or villagers from one location to another. It's actually quite simple.
Just like you can fish by right-clicking water, just right-click a mob (you don't even need to be directly next to the mob, so long as the bobber can reach the mob) and the mob will be sent to your caught mob list. To put them in a new area, simply left-click the target block (must be the top face of a block, or directly on the surface) and the mobs will be transported to the new location.
To clear your caught mob list, type /cca, or /clearcaughtanimals.
This only works on areas that aren't lots, or lots that you own.